cesphil
Active Member
- Joined
- Jan 30, 2012
- Messages
- 147
- Location
- Tampa
- Aircraft
- Cessna 150 and Dominator
- Total Flight Time
- 960
There have been many posts on this forum recently regarding yaw and torque effects on the stability and controllability of a gyroplane. In particular, due to several recent “Euro-Tub” crashes, posters have been trying to analyze and explain how torque and P-factor can generate an undesired roll or yaw in a gyroplane. Many of these posts have confused P-factor with gyroscopic precession. While both create a change in yaw due to a change in pitch (or vice versa), they are different dynamics and create opposite reactions for different reasons.
Let’s analyze what happens to a gyroplane when the nose is suddenly pitched up. For this example, we will use a pusher type gyroplane with the engine turning clockwise when viewed from the rear.
Most are familiar with engine torque and understand that it will cause a roll to the left so we won’t dwell on this. Do note that the torque is a product of engine power and is not a result of the upward pitch.
Now, let’s talk about gyroscopic precision. Remember in high school physics when the teacher handed you a spinning bicycle wheel with a handle on each end of the axle. When you tried to tilt the wheel, it reacted different to your expectation. The instructor was demonstrating “gyroscopic precession”. Gyroscopic precession causes a force to act at 90 degrees of rotation to the applied force. If the nose of the gyroplane is suddenly pitched upward, we are moving to top of the propeller rearward and the bottom of the propeller forward. With the propeller rotating clockwise (from the rear), gyroscopic precession will move the right side of the propeller rearward and the left side of the propeller forward which will yaw the aircraft to the right.
Now, we get to P-factor. I have seen posts in this forum where gyroscopic precession was incorrectly explained as P-factor. I have attached a publication by the FAA that explains; torque, gyroscopic precession and P-factor. I find their explanation of P-factor a little unclear so I have produced a drawing (PF-1) that I hope will help explain it.
When an aircraft is flying straight and level, the propeller is perpendicular to the direction of travel so the propeller blades see the same relative wind and have the same angle of attack in any location as they rotate around the crankshaft (or the propeller axis). As a result, the propeller is producing the same amount of forward lift (or thrust) at any point in its rotation, thus producing symmetrical thrust. If the aircraft were suddenly pitched upward while still traveling in a straight and level direction, the propeller axis is no longer parallel with the direction of travel (relative wind) so the angle of attack of a propeller blade varies with a position of the blade as it rotates about the axis. The downward blade will have a greater angle of attack while the upward blade will have a lesser angle of attack. As a result, the downward blade, which is on the right side of our clockwise rotating prop, will generate more push and yaw the aircraft to the left.
It is interesting to note that gyroscopic precession and P-factor counter act one another, so obviously one of the two will need to produce a more powerful action in order to generate a yaw. I will leave my explanation as such and let the debaters take it from here.
Let’s analyze what happens to a gyroplane when the nose is suddenly pitched up. For this example, we will use a pusher type gyroplane with the engine turning clockwise when viewed from the rear.
Most are familiar with engine torque and understand that it will cause a roll to the left so we won’t dwell on this. Do note that the torque is a product of engine power and is not a result of the upward pitch.
Now, let’s talk about gyroscopic precision. Remember in high school physics when the teacher handed you a spinning bicycle wheel with a handle on each end of the axle. When you tried to tilt the wheel, it reacted different to your expectation. The instructor was demonstrating “gyroscopic precession”. Gyroscopic precession causes a force to act at 90 degrees of rotation to the applied force. If the nose of the gyroplane is suddenly pitched upward, we are moving to top of the propeller rearward and the bottom of the propeller forward. With the propeller rotating clockwise (from the rear), gyroscopic precession will move the right side of the propeller rearward and the left side of the propeller forward which will yaw the aircraft to the right.
Now, we get to P-factor. I have seen posts in this forum where gyroscopic precession was incorrectly explained as P-factor. I have attached a publication by the FAA that explains; torque, gyroscopic precession and P-factor. I find their explanation of P-factor a little unclear so I have produced a drawing (PF-1) that I hope will help explain it.
When an aircraft is flying straight and level, the propeller is perpendicular to the direction of travel so the propeller blades see the same relative wind and have the same angle of attack in any location as they rotate around the crankshaft (or the propeller axis). As a result, the propeller is producing the same amount of forward lift (or thrust) at any point in its rotation, thus producing symmetrical thrust. If the aircraft were suddenly pitched upward while still traveling in a straight and level direction, the propeller axis is no longer parallel with the direction of travel (relative wind) so the angle of attack of a propeller blade varies with a position of the blade as it rotates about the axis. The downward blade will have a greater angle of attack while the upward blade will have a lesser angle of attack. As a result, the downward blade, which is on the right side of our clockwise rotating prop, will generate more push and yaw the aircraft to the left.
It is interesting to note that gyroscopic precession and P-factor counter act one another, so obviously one of the two will need to produce a more powerful action in order to generate a yaw. I will leave my explanation as such and let the debaters take it from here.